To increase a throughput of a UE (user equipment), in a macro cell, a plurality of small stations may be introduced to form a small cell, and a small cell can cover a hotspot region or cover a hole region. In this way, when a UE moves to these regions covered by small cells, a service of the UE can be switched to these small cells to implement service offload or coverage compensation. These small stations may be small base stations, micro base stations, home base stations, RRHs (remote radio heads), or relay stations.
For example, in an existing CA (carrier aggregation) technology, an RRH is located under coverage (for example, a hotspot region) of a base station, and the RRH and the base station have different frequencies. A backhaul manner of an optical fiber connection is adopted between the RRH and the base station, and an optical fiber has characteristics such as a low delay and a large bandwidth. When a UE is under coverage of the RRH, the base station performs centralized scheduling, and the base station and the RRH transmit data to the UE at the same time in a carrier aggregation manner, thereby increasing a throughput of the UE.
In another example, in an existing CoMP (coordinated multiple points transmission) technology, an RRH is located under coverage (for example, a hotspot region) of a base station, and the RRH and the base station have a same frequency. A backhaul manner of an optical fiber connection is adopted between the RRH and the base station, and an optical fiber has characteristics such as a low delay and a large bandwidth. When a UE is under coverage of the RRH, the base station performs centralized scheduling, and the base station and the RRH coordinate to transmit data to the UE to increase a throughput of the UE.
In the foregoing existing mechanisms, the base station performs centralized scheduling and processing. Specifically, a protocol layer of the base station includes: a PDCP (packet data convergence protocol) layer, an RLC (radio link control) layer, a MAC (medium access control) layer, a Phy (physical) layer, and the like. The base station encapsulates a data packet and allocates a radio resource and then sends, through an optical fiber, the encapsulated data packet and the radio resource used by the RRH to the RRH. The rapid transmission of an optical fiber has almost a zero delay, guaranteeing that the RRH sends the encapsulated data packet to the UE on a radio interface based on an order that the base station schedules the RRH and the radio resource. Therefore, the UE is capable of decoding correctly, and confusion does not occur.
However, a backhaul link deployed with an optical fiber has high cost. For carriers who demand lower cost, a backhaul link deployed with an optical fiber is an excessively ideal network. In existing networks of many carriers, most are ordinary backhaul links, such as an Ethernet, an xDSL (digital subscriber line), or microwave. An ordinary backhaul link has a larger delay (for example, 10 ms to 20 ms) and a smaller bandwidth compared with an optical fiber backhaul link. If the CoMP or CA technology is adopted, data scheduled by a base station needs to be transmitted through a backhaul link to each RRH for subsequent transmission. As delays from the base station to RRHs are different, the base station practically cannot effectively control the moment of sending data, which might cause that data of two RRHs is transmitted on one same radio resource, resulting in strong interference and further a failure in implementing CoMP or CA. Also, for CoMP or CA, data that a base station transfers to an RRH through a backhaul link is modulated, encoded, and the like, and a size of data becomes larger, which occupies a larger bandwidth and forms a great challenge for an ordinary backhaul link.
Therefore, in an ordinary backhaul link, due to limits of delay and bandwidth for a backhaul link of a carrier, an RRH cannot be deployed to implement multiple points transmission. The problem to be solved by the present disclosure is how to implement multiple points transmission by lowering a delay requirement on a backhaul link based on an existing limited backhaul link.